脈寬調變抖動對切換式電源轉換器之效率影響

Abstract

一些原因使得切換式電源轉換器導致脈寬調變抖動，如降低電磁干擾和高頻寬的設計方案。本論文主旨為提出兩種效率模型適用於分析脈寬調變抖動對切換式電力轉換器之影響: 平均效率模型與多頻率效率模型。本文首先藉由電路模型推導，將傳統小訊號模型中所忽略的兩個擾動訊號源之乘積納入考量，進而推衍出一個新的平均效率模型。然而由於脈波寬度比較器之增益為非線性，本文進一步藉由多頻率小訊號模型為基礎，推衍並補足既有的多頻率小訊號模型，發展出一個新穎之多頻率效率模型。本文所提出之多頻率效率模型可以涵蓋平均效率模型外，並具有可適用於高頻訊號、任意週期性波形訊號分析之特點。本文最終也提出脈寬調變抖動對切換式電力轉換器效率下降的建議方案。此外本文也藉由數學推導與圖示，來說明一般電力電子轉換器於量測穩定度時，其波德圖曲線在開關切換頻率之整倍頻的突波現象。最後，以電腦模擬與測試機台來驗證與所提出的效率模型相符。

There are several reasons to cause the PWM jitter in power converter such as EMI reduction, and the side effect of high bandwidth design. The primary objective of this dissertation is to propose two efficiency models for evaluating the impact of the PWM jitter on the efficiency of switching-mode power converter: average efficiency model and the multi-frequency efficiency model. By taking the product of two perturbation terms into consideration, which is ignored in the conventional average small-signal model, the average efficiency model is proposed first. Due to the nonlinear characteristic of the PWM comparator, the multi-frequency efficiency model is also developed by considering the sideband frequency. The proposed multi-frequency efficiency model not only covers the average efficiency model but also apply for high frequency signal and arbitrary periodic wave. Eventually, the methods to reduce the efficiency impact caused by the jitter are suggested. In addition, the reason of control-to-output gain’s magnitude spike on the Bode plot can be explained by the derived equations. In spite of various perturbation frequencies, amplitudes, and waveforms, the mathematical calculation, the computer simulation, and the hardware measurement of the efficiency impact are consistent which validate the accuracy of the proposed multi-frequency efficiency model.